For critics, it's better to be interesting than right

The naked and the fed ... The Odalisque (1745) is typical of François Boucher's portraits of decadence. Photograph: The Gallery Collection/Corbis

Art criticism has a history that is almost as long as the history of art itself. In his Naturalis Historia, written in the first century AD, the Roman author Pliny the Elder discusses the lives and works of painters and sculptors. Not quite art criticism as you find it in a modern newspaper, maybe, but he does rail that "a fatal malaise has taken hold of the arts".

The real birth of modern art criticism is usually traced to 18th-century France. It started at the moment art addressed a wide and potentially universal audience: "the public". Instead of pleasing the court and king, 18th-century French artists appealed directly to public opinion at the hugely popular Salon exhibitions. Critics, reviewing these shows, started to make themselves heard. Today, the most famous of these 18th-century critics is Denis Diderot, the Enlightenment philosopher who also wrote passionately about his loves and hates in contemporary art.

Diderot raises a question: is a good critic one who is right, or one who makes an interesting case, however wrong-headed? He loathed the sensuous, sophisticated, courtly and erotic painter François Boucher. In his eyes, Boucher's paintings were heartless, decadent, trivial, and morally worthless.

In place of Boucher he preferred another contemporary, Jean-Baptiste Greuze. For Diderot, this painter of grief-stricken families and sincere young people was a truly serious and worthwhile artist – the antithesis of Boucher.

A good place to compare these two artists is the Wallace Collection in London, which has works by both in abundance. Boucher's erotic mythological fantasies are floating concoctions of silk and skin, ethereal and flimsy and ... hugely pleasurable. He is defiantly unserious and delightfully ambitious in the scale and proliferation of his visual frolics. As for Greuze – what visitor to the Wallace Collection spends much time on this sentimental, morbid, palpably dishonest artist's clogged and nauseating daubs?

Well, that's changing taste for you. There were compelling reasons for Diderot to see so much more in Greuze that meets our eyes. He was setting out a theory of art, searching for a definition of value that was truly serious, moral, even political. His readers were searching too, which was why they too loved Greuze.

What does all that have to with art and criticism today? Everything. The job of a critic is not to be "right" – that would make them into jumped-up authority figures, high-court judges of art. What pompous nonsense. The memorable critics – including the greatest of all, John Ruskin – were often wrong, even absurd, but they made arguments that will always bear thinking about. Ruskin could pursue a train of thought over hundreds of pages and his richness of intellect and language makes the journey worthwhile, even if you find his opinions insane or offensive.

Critics are not parasitical on art. They practice an art of their own. History shows that being right has very little to do with it.